Boron nitride (“BN”) comes in a variety of crystalline structures and has a variety of uses from polishing agents to lubricants. Hexagonal boron nitride (“hBN”) has a hexagonal layer structure similar to graphite. Because of its properties, it has found uses in heat conductivity applications, electrical insulation applications, corrosion resistance applications, lubrication applications, personal care applications, and as a plastic additive. In the prior art, white powders of BN particles with platelet morphology and hexagonal structure similar to that of graphite may be manufactured in a high temperature reaction from inorganic raw materials.
Because of h-BN particles' platelet morphology, polymer compositions containing h-BN particles usually have much higher viscosities than ones containing spherical alumina of comparable volume loadings. When platelet BN is added as a filler to a polymer, a blended material is formed having poor rheological properties. At loadings above 30 wt. % BN, the blended material is so viscous that it is difficult to dispense it from a mechanical dispenser such as a syringe. Particle settlement is also more pronounced in hBN-filled silicone composites than in alumina-filled ones, even though hBN has a much lower density than alumina. To alleviate both the viscosity and the filler separation problems, surface treatment of hBN has been tried.
U.S. Pat. No. 6,731,088 discloses a process to manufacture BN, forming a dry powder of spherically shaped agglomerates of irregular non-spherical particles bound together by a binder and subsequently spray-dried. The spherically shaped BN agglomerates can be combined with polymers at levels of 35-50 wt. % to form compositions with viscosity below about 300 cp. JP Publication No. 05-051540 discloses BN powder treated with at least a titanate coupling agent, a silane coupling agent, and a non-inonic coupling agent in an amount of 0.1 to 5 wt. %, to improve the wettability of the BN in applications such as a release agent, a lubricant, a low-friction material, a coating material, etc. U.S. Pat. No. 6,162,849 discloses a thermally conductive moldable polymer blend having at least 60 wt. % of BN powder having an average particle size of at least 60 microns and coated with a coupling agent, and wherein the thermally conductive composition has a thermal conductivity of at least 15 W/m° K.
In addition, BN powder is known to degrade in humid conditions. It may therefore be useful to treat BN powders to render it more hydrophobic.
There is still a need for improved BN compositions, particularly for BN compositions that can be used in large quantities as a filler in applications including but not limited to automotive and electronic applications as well as for BN particles that withstand humid conditions.